In just a few years, green roofs have gone from a horticultural curiosity to a booming growth industry - primarily because the environmental benefits of extensively planted roofs are now beyond dispute, whether for industrial or governmental complexes or for private homes in urban or suburban settings. Despite the high level of interest in green roofs, until now there has been no reliable reference devoted exclusively to the various species of drought-tolerant plants that are suitable for use on extensive green roofs. Green Roof Plants fills that void. The book contains photographs and cultural information for more than 200 species and cultivars of plants, including valuable data on moisture needs, heat tolerance, hardiness, bloom color, foliage characteristics, and height. Concise, accurate, and easy to use, this book is destined to become an indispensable practical reference guide, not just for architects, landscape designers, engineers, and environmentalists, but also for environmentally conscious home gardeners.

The idea of greening a roof is not a new one and, in fact, dates back thousands of years. Civilizations in Mesopotamia originated the concept (Dunnett and Kingsbury 2004), and Greeks, Romans, Persians, and other cultures had some form of roof gardens to green and cool their often brutally hot landscapes. The famed "hanging gardens of Babylon," for example, were actually planted on rooftops. At the other climatic extreme, sod roofs have long graced homes in Scandinavia, providing extra warmth and insulation in cold, wet climates. Nature itself is the inspiration for green roofs, depositing seeds that germinate in leaf, dirt, and rock piles on garden sheds, in gutters, and on seemingly inhospitable, often flat, stretches of roof. Green roofs did not attain widespread use until more recent times, and then only in parts of northern Europe, where the scarcity of land for new buildings, combined with the development of new roofing materials like concrete, were driving forces behind their modern adaptation. When Switzerland, Germany, Austria, and other countries embarked on a post-World War II building campaign, they utilized green roofs for practical, environmental, and aesthetic purposes. As cities expanded to the edges of the countryside, green roofs represented an innovative way to preserve green space, reduce the impact of development, and help filter and purify the air. Planted roofs increased oxygen output, softened urban streetscapes, reduced impervious surfaces, and contained storm water runoff to vital tributaries and major bodies of water that supplied drinking water to millions of people.